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<ul id="index">
  <li><a href="#NAME">NAME</a></li>
  <li><a href="#SYNOPSIS">SYNOPSIS</a></li>
  <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
  <li><a href="#NOTES">NOTES</a></li>
  <li><a href="#RETURN-VALUES">RETURN VALUES</a></li>
  <li><a href="#EXAMPLES">EXAMPLES</a></li>
  <li><a href="#SEE-ALSO">SEE ALSO</a></li>
  <li><a href="#HISTORY">HISTORY</a></li>
  <li><a href="#COPYRIGHT">COPYRIGHT</a></li>
</ul>

<h1 id="NAME">NAME</h1>

<p>EVP_PKEY_decapsulate_init, EVP_PKEY_auth_decapsulate_init, EVP_PKEY_decapsulate - Key decapsulation using a KEM algorithm with a private key</p>

<h1 id="SYNOPSIS">SYNOPSIS</h1>

<pre><code>#include &lt;openssl/evp.h&gt;

int EVP_PKEY_decapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
int EVP_PKEY_auth_decapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpub,
                                  const OSSL_PARAM params[]);
int EVP_PKEY_decapsulate(EVP_PKEY_CTX *ctx,
                         unsigned char *unwrapped, size_t *unwrappedlen,
                         const unsigned char *wrapped, size_t wrappedlen);</code></pre>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

<p>The EVP_PKEY_decapsulate_init() function initializes a private key algorithm context <i>ctx</i> for a decapsulation operation and then sets the <i>params</i> on the context in the same way as calling <a href="../man3/EVP_PKEY_CTX_set_params.html">EVP_PKEY_CTX_set_params(3)</a>. Note that <i>ctx</i> usually is produced using <a href="../man3/EVP_PKEY_CTX_new_from_pkey.html">EVP_PKEY_CTX_new_from_pkey(3)</a>, specifying the private key to use.</p>

<p>The EVP_PKEY_auth_decapsulate_init() function is similar to EVP_PKEY_decapsulate_init() but also passes an <i>authpub</i> authentication public key that is used during decapsulation.</p>

<p>The EVP_PKEY_decapsulate() function performs a private key decapsulation operation using <i>ctx</i>. The data to be decapsulated is specified using the <i>wrapped</i> and <i>wrappedlen</i> parameters. If <i>unwrapped</i> is NULL then the size of the output secret buffer is written to <i>*unwrappedlen</i>. If <i>unwrapped</i> is not NULL and the call is successful then the decapsulated secret data is written to <i>unwrapped</i> and the amount of data written to <i>*unwrappedlen</i>. Note that, if <i>unwrappedlen</i> is not NULL in this call, the value it points to must be initialised to the length of <i>unwrapped</i>, so that the call can validate it is of sufficient size to hold the result of the operation.</p>

<h1 id="NOTES">NOTES</h1>

<p>After the call to EVP_PKEY_decapsulate_init() algorithm-specific parameters for the operation may be set or modified using <a href="../man3/EVP_PKEY_CTX_set_params.html">EVP_PKEY_CTX_set_params(3)</a>.</p>

<h1 id="RETURN-VALUES">RETURN VALUES</h1>

<p>EVP_PKEY_decapsulate_init(), EVP_PKEY_auth_decapsulate_init() and EVP_PKEY_decapsulate() return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the private key algorithm.</p>

<h1 id="EXAMPLES">EXAMPLES</h1>

<p>Decapsulate data using RSA:</p>

<pre><code>#include &lt;openssl/evp.h&gt;

/*
 * NB: assumes rsa_priv_key is an RSA private key,
 * and that in, inlen are already set up to contain encapsulated data.
 */

EVP_PKEY_CTX *ctx = NULL;
size_t secretlen = 0;
unsigned char *secret = NULL;;

ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_priv_key, NULL);
if (ctx == NULL)
    /* Error */
if (EVP_PKEY_decapsulate_init(ctx, NULL) &lt;= 0)
    /* Error */

/* Set the mode - only &#39;RSASVE&#39; is currently supported */
if (EVP_PKEY_CTX_set_kem_op(ctx, &quot;RSASVE&quot;) &lt;= 0)
    /* Error */

/* Determine buffer length */
if (EVP_PKEY_decapsulate(ctx, NULL, &amp;secretlen, in, inlen) &lt;= 0)
    /* Error */

secret = OPENSSL_malloc(secretlen);
if (secret == NULL)
    /* malloc failure */

/* Decapsulated secret data is secretlen bytes long */
if (EVP_PKEY_decapsulate(ctx, secret, &amp;secretlen, in, inlen) &lt;= 0)
    /* Error */</code></pre>

<h1 id="SEE-ALSO">SEE ALSO</h1>

<p><a href="../man3/EVP_PKEY_CTX_new_from_pkey.html">EVP_PKEY_CTX_new_from_pkey(3)</a>, <a href="../man3/EVP_PKEY_encapsulate.html">EVP_PKEY_encapsulate(3)</a>, <a href="../man7/EVP_KEM-RSA.html">EVP_KEM-RSA(7)</a>, <a href="../man7/EVP_KEM-X25519.html">EVP_KEM-X25519(7)</a>, <a href="../man7/EVP_KEM-EC.html">EVP_KEM-EC(7)</a></p>

<h1 id="HISTORY">HISTORY</h1>

<p>The functions EVP_PKEY_decapsulate_init() and EVP_PKEY_decapsulate() were added in OpenSSL 3.0.</p>

<p>The function EVP_PKEY_auth_decapsulate_init() was added in OpenSSL 3.2.</p>

<h1 id="COPYRIGHT">COPYRIGHT</h1>

<p>Copyright 2020-2024 The OpenSSL Project Authors. All Rights Reserved.</p>

<p>Licensed under the Apache License 2.0 (the &quot;License&quot;). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>


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